In order to assure the physiological status of small experimental animals, pulmonary and circulatory functions must be monitored accurately and frequently. Arterial blood-gas measurements are critical for this monitoring, however, repeated measurements can affect blood volume and hematocrit, especially in small animals. This project will develop reagents and instrumentation to continuously monitor arterial blood gases and pH in the peripheral circulation of small mammals. Microspheres, designed to change their luminescent emission lifetimes in response to blood gases and pH, will be injected into peripheral the arterial circulation. Blood-gas parameters will be recorded by measuring lifetime changes of phosphorescent dyes in trapped microspheres. The microspheres and instrumentation developed by this project will be suitable for continuous monitoring of arterial-blood gases and pH for both acute studies and for periodic measurements of arterial-blood parameters for chronic studies lasting several months. Phase I research will develop oxygen-sensitive microspheres and will test instrumental methods to measure their phosphorescent properties in situ. The experimental success of this approach will be evaluated by measuring arterial PO2 noninvasively in the extremities of rats. Phase II research will extend the capabilities of labeled microspheres to measurements of pH and PCO2.